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Discussion
In accordance with our previous results (cf. Introduction), a
plausible conclusion is that the observed transformations of the
state of the studied multicomponent model oil are governed by
equilibrium-metastable transitions in asphaltene colloids.
A schematic description may be that at ≈28°C a structural
transformation occurs in basic “molecular nanoclusters” (MNCs) of
asphaltenes. As a result, MNC–MNC interactions become some-
what stronger, while interactions of MNCs with solvent molecules
become somewhat weaker. Consequently, steric stabilization of as-
phaltene colloids by resins is disrupted and directly interacting
MNCs may form more complex aggregates, fairly long-lived at
lower temperatures.
For a given concentration (volume fraction) of asphaltenes,
formation of complex deformable aggregates may indeed result in a
lower viscosity, as follows from rheological theories for suspensions
of deformable particles (e.g. Brenner, 1975; Manga et al., 1998, and
references therein). This viscosity decrease by itself may facilitate
a transport of depositing material to a metal surface and may be
responsible (at least partially) for the observed increase in the
mass of deposits from the oil in a metastable (transient) state. An-
other reason for increased deposition may be the presumed higher
activity of structurally transformed asphaltene MNCs.
Literature analysis has revealed some experimental results by
other authors in favour of our basic assumption that the observed
specific temperature of ≈28°C is singled out by the processes in-
volving solely asphaltenes and not other constituents of our multi-
component model oil. It should be emphasised that in respective
publications the existence of this specific temperature remained
unnoticed by the authors.
E.g. Ramos et al., 2001 measured viscosities and surface ten-
sions as functions of concentration of pure C5I and C7I asphalte-
nes in various solvents. The inflections on concentration dependen-
cies they ascribed to a “critical micelle concentration” (CMC) and to
a “second aggregation concentration” (SAC). In Tables 1,2 of their
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